The present invention broadly relates to non-contact inspections systems and methods, and deals more particularly with a method and apparatus for inspecting the surface of semiconductor device such as a semiconductor wafer.
In connection with processes used to fabricate semiconductor devices, such as semiconductor wafers, uniformity and consistency from device-to-device, and from batch-to-batch are critical in achieving high yield and superior device quality. A series of successive processes are carried out in order to complete fabrication of a semiconductor wafer. These processes rely on carefully controlled processing parameters, as well as controlled processing environments in order to achieve high quality wafers. Nevertheless, some variations do occur during the fabrication process that can result in one or more localized defects in the surface of the wafer. When the wafer is sliced into individual die, those die within the localized defect are must be discarded, thus resulting in scrap and reduced yield. It is therefore critical in such fabrication processes to identify, through some means of inspection, those localized areas on the wafer which contain defects. Such defects may be as the result of too little or too great of material coating thickness within certain areas on the wafer, or as the result contaminants having been deposited on the wafer surface.
In the past, wafer surface quality, uniformity and defects were assessed using purely visual means, wherein an operator would place the wafer under a microscope and view the wafer surface under magnification to identify localized defect areas. This manual process was not only time consuming and tedious, but was not always entirely effective in identifying defects. Although non-contact inspections systems have long been used in semiconductor manufacturing processes to aid in determining the position and placement of components or certain features on a device surface, such inspection methods are not suitable for use in identifying surface defects on a semiconductor wafer.
Accordingly, there is a clear need in the art for an improved inspection method and apparatus which overcome each of the shortcoming of the prior art discussed above.
According to one aspect of the invention, a method is provided for inspecting the surface of a semiconductor device, such as a semiconductor wafer, which comprises the steps of: directing a beam of light through an optical element onto the surface of a semiconductor device; receiving light reflected from a surface which originates from the optical element; measuring a characteristic of the received light; and, scanning the surface of the device while relatively moving the device and the optical element.
The light is preferably formed in a curtain defining a line of light impinging on the device surface, and the relative movement is preferably produced by rotating the line of light about an axis essentially perpendicular tot he surface of the device. The reflected light is preferably passed through an optical receiver or detector which is rotated relative to the semiconductor device, in synchronization with a light beam, also about an axis perpendicular tot he surface of the device. In order to aid in precisely locating the surface defects, reference marks are applied to the device surface which are detected during the scanning process and provide a frame of reference for locating defects.
According to another aspect of the invention, a method for inspecting the surface of a semiconductor device is provided, which comprises the steps of: rotating a curtain of light impinging on the surface of the wafer such that the wafer surface is scanned by the light; rotating an optical receiver in synchronization with the rotation of the light curtain; receiving light in a receiver which is reflected from the surface of the wafer; and, analyzing the light received by the optical receiver.
The analysis is preferably performed by measuring the amplitude of the received light as a function of a rotational position of the optical receiver.
According to still another aspect of the invention, apparatus is provided for inspecting the surface of a semiconductor wafer which comprises; light source means for directing a line of light onto the surface of the wafer; an optical light receiver for receiving light reflected from the surface and originating from the light source; means for rotating the light and the receiver about an axis essentially perpendicular to the wafer; and, means for analyzing the light received by the receiver. The optical receiver preferably includes a linear photosensor array. Means are provides for locatably mounting the light source and a receiver, and motor means are provided for rotating the mounting means.
According to still another aspect of the invention, apparatus is provided for inspecting the surface of a semiconductor wafer comprising: first and second light sources for respectively directing first and second lines of light on to the surface of the wafer; first and second optical receiver for respectively receiving light reflected from the wafer surface and originating from the light sources; mans for analyzing the light received by the optical receiver; means for mounting the light sources and receivers as a single, common assembly; and, means for rotating the assembly about an axis extending essentially perpendicular to the wafer surface.
Accordingly, it is the primary object of the present invention to provide a method and apparatus for inspecting the surface of a semiconductor wafer.
A further object of the invention is to provide a method and apparatus as described above which provides highly reliable inspection results which are superior to that attainable by manual, visual inspection.
A still further object of the present invention is to provide a method and apparatus as aforementioned, in which the inspection process is performed quickly and automatically.
Another object of the present invention is to provide a method and apparatus as described above which allows complete automation of the inspection process so as to be suitable for inspecting a plurality of semiconductor wafers in rapid succession.
Another object of the present invention is to provide a method and apparatus of the type mentioned above which allows locating, with high precision, and recording the location of surface defects.
These, and further objects and advantages of the invention will be made clear or will become apparent during the course of the following description of the preferred embodiment of the present invention.